The prevalence of Parkinson's disease (PD) is increasing and predicted to double in the US and more than double in developing countries during the next 25 years; however a definite etiology or unifying sequence of molecular events for the most common form of PD, late onset sporadic idiopathic PD, has not been established. The long term goal of this project is to delineate mechanisms of environmental agents that contribute to increased risk for PD. The ubiquitin pathway has been implicated as a target for environmental agents based upon familial forms of PD resulting from loss of function mutations in Parkin and UCHL1 that are both components of the ubiquitin pathway. The experiments presented in this application are guided by the following working Hypothesis: The triazine and thiocarbamate herbicides, and the diaklydithiocarbamate and benomyl based fungicides covalently modify and inhibit UBA1 activating enzyme resulting in impaired ubiquitin based protein processing and cell signaling that promote neurodegenerative changes contributing to PD. This hypothesis will be tested through the following Specific Aims: 1) To determine in vivo in rats if the proposed pesticides or selected metabolites inhibit UBA1 activating enzyme and produce nigrostriatal toxicity. To achieve this aim we will determine the dose-response for brain UBA1 enzyme inhibition, characterize UBA1 covalent modifications by shotgun LC/MS/MS, map neurodegenerative changes and quantify the expression and phosphorylation of tau and -synuclein. 2) To determine if in vitro inhibition of UBA1 contributes to dopaminergic neuron cytotoxicity, activation of Cdk5 and altered processing of gene products associated with sporadic PD. To achieve this aim MN9D cells will be used to modulate UBA1 expression and determine the influence of constitutively compromised and increased UBA1 function on viability, the expression and phosphorylation state of -synuclein and tau proteins, activation of Cdk5 and expression and localization of the dopamine transporter in cells exposed to the proposed pesticides, their metabolites or specific pharmacologic UBA1 inhibitors. The data derived from the proposed studies will assist in the formulation of more informed risk management and the development of screening methods to identify and predict other agents that act through similar or additive mechanisms. Identification of environmental agents that contribute to the development of PD either directly or through gene-environment interactions will facilitate strategies of intervention to decrease the risk of PD and slow the progression of disease in PD patients.